Source: Comic Koh Vol. 6: https://e-hentai.org/g/879307/c010271cbf/. I accidentally used the lower quality raws and only found out after cleaning and typesetting most pages ;-;.
The art looks old school. Like from romance mangas from the late 80s or early 90s. Btw, what the fuck means that "however..." at the end? The story was wholesome but suddenly that single word made it unsettling.
@8o8o8o8o as you can see, it's a manga, not a doujin.
tearsax there are a few possibilities as I see it, either she is referring to the fact that she is going away for college so they can't really have a relationship, the fact that it may not have been enough for her given that she called him weak even after he came 6 times, or there are some consequences on her end that are not expressed directly in the work like a possibility that she has a boyfriend that her childhood friend the MC doesn't know about.
The last one is possible because of the supporting evidence. She has numerous condoms on her, something even the MC took notice of on page 14 of the gallery. She was not a virgin as there is no mention of it, she was really experienced and even dominant during the sex, and there is no defloration tag. Finally she seems to be acting as a pure innocent girl in front of him as implied by her statement on page 17 of the gallery. Also the glance and self remark of seeing him in the window on page 1 could imply either feelings for him, or a sense of guilt that she is keeping a secret, more likely the latter as there is no blush to represent embarrassment.